Light-sensitive photographic paper

ABSTRACT

PHOTOGRAPHIC PAPER BASE IS SIZED WITH A DISPERSION OF CROSS-LINKED VINYL ACETATE POLYMER TO AVOID MOTTLE, OBTAIN IMPROVED STIFFNESS AND OTHER PROPERTIES.   D R A W I N G

June 1, 1971 w. H. GRIGGS El'AL 3,582,337

LIGHT-SENSITIVE PHOTOGRAPHIC PAPER Filed June 27, 1968 PHOTOGRAPH/GEMULSION LAYER GROSS-LINKED VINYL ACETATE POLYMER SIZING PHOTOGRAPH/GEMULSION LAYER POLYETHYLENE \mass-umxw VINYL my; mrs POLYMER s/znva l2,P-POL YETH YLENE F/ 3 /BLUE SENSITIVE EMULSION LAYER GREEN SENSITIVEEMULSION LAYER RED SENSITIVE EMULSION LAYER .4 "'A POL YETH YLENE mass L//VKED v//v YL PAPER ACETATE POLYMER SIZING POLYETHYLENE WILLIAM H.GRIGGS MERLE K. ELDRIDGE DAVID R. FULTON INVENTORS A GEN T United StatesPatent Office 3,582,337 Patented June 1, 1971 3,582,337 LIGHT-SENSITIVEPHOTOGRAPHIC PAPER William H. Griggs, Rochester, Merle K. Eldridge,Hilton, and David R. Fulton, Rochester, N.Y., assignors to Eastman KodakCompany, Rochester, N.Y.

Filed June 27, 1968, Ser. No. 740,581 Int. Cl. G03c 1/86 US. C]. 96-85 9Claims ABSTRACT OF THE DISCLOSURE Photographic paper base is sized witha dispersion of cross-linked vinyl acetate polymer to avoid mottle,obtain improved stiffness and other properties.

This invention relates to the production of paper particularly suitablefor use as a photographic paper base.

The use of paper as a base or support for light-sensitive photographicemulsions is well konwn in the art. A wide range of weight of papers isused for this purpose, for example, papers weighing from about to 60pounds per 1,000 square feet. The lightweight papers are particularlyuseful Where it is desired to wind the maximum footage of sensitizedpaper on a spool. However, it is usually necessary to heavily tub sizethe lightweight papers to obtain the wet and dry stiffness desired or toobtain a stiffness actually required by apparatus in which the paper isto be handled. Often tub sizing is not adequate to obtain the desiredstiffness and the weight of the paper must be increased. In thephotographic art, in addition to imparting stiffness to the paper, thesize should reduce penetration to aqueous solutions such as theconventional acid and alkaline photographic processing solutions. Alsothe sizing must produce a surface inert to the light-sensitive coatingapplied thereto. Moreover, the light-sensitive coating must coatuniformly onto the sized paper surface, for example, to avoid theproduction of light-sensitive coatings containing mottle. A silverhalide emulsion layer which is subjected to an overall even exposure anddeveloped to provide an image should have even density throughout. Ifit, instead, exhibits areas having distinctly higher or lower densitythan that of the remaining areas of the image, it may be said to havemottle. The areas having the higher or lower density exhibit densitiesof greater difference than would be expected or predicted from thephotographic speed of the particular system.

We have discovered a method for tub sizing photographic paper base whichimparts unexpected properties to the paper in addition to improvedstiffness. Our process involves tub sizing this paper with an aqueouslatex of an emulsion polymerized mixture of vinyl acetate and across-linking monomer such as N-methylol acrylamide or hydroxyethylacrylate. The cross-linking monomer is, thus, a polymerizable vinylcompound'containing the vinyl group for copolymerizing with the vinylacetate. In addition, the monomer contains a lower hydroxyalkyl group,such as a hydroxyethyl or methylol, capable of reaction with similargroups on other copolymer chains in the reaction mixture to produce acrosslinked polymer latex. As a result, papers of improved stiffness areobtained and sensitive coatings applied thereto are free of mottle evenwhen lightweight paper stocks have been used. Resistance to solutionpenetration is also good. The sized paper surface has no adverse effecton the light-sensitive layers. It is probable that these advantageousproperties obtained in the tub-sized paper result in part from reactionof residual methylol or other hydroxyalkyl groups of the cross-linkedvinyl acetate polymer with similar groups present on the cellulosemolecules of the paper base. A three-dimensional structure involving thepolymer chains and cellulose chains is, thus, obtainable.

Many naturally-occurring and synthetic polymeric materials have beenproposed for tub sizing paper and have been more or less successful forthe intended purpose. However, none of these polymers have possessed thecombination of properties necessary to produce photographic paper baseof the desired stiffness at low caliper and which paper base is inert tophotographic emulsions and is uniformly coated by photographicemulsions. These polymers have often resulted in a paper sheet whichtends to be sticky. Often the polymers would fog silver halide emulsionscoated thereon. The present cross-linked vinyl acetate polymer laticesare unique in imparting the mentioned desirable properties to the paperbase.

Cross-linking vinyl monomers containing a lower hydroxyalkyl groupespecially useful for emulsion polymerization with vinyl acetate are:N-methylol acrylamide, N-methylol methacrylamide, glycidyl acrylate,glycidyl methacrylate, hydroxyethyl acrylate, hydroxyethyl methacrylate,hydroxpropyl acrylate or hydroxypropyl methacrylate. The cross-linkingmonomer is used particularly in an amount necessary to obtain thedesired hardness in the vinyl acetate polymer and stiffness in thepaper. About 0.5 to 10% by weight of the cross-linking monomer is usefulwith about 99.5 to by weight of vinyl acetate. N-methylol acrylamide andN-methylol methacrylamide are especially useful for emulsionpolymeriza-- tion with vinyl acetate in these proportions. The emulsionpolymerization is carried out in water in a well-known manner by heatingin the presence of a surfactant and catalyst so as to produce a latex ofabout 40-50% solids by weight. The surfactant and catalyst are selectedso as to be photographically acceptable, i.e., inert to lightsensitivephotographic layers. Anionic surfactants such as sodium lauryl sulfonateare useful. Water-soluble catalyst, e.g. potassium persulfate, can beused with heating to about 70 C. or sodium meta-bisulfate with potassiumpersulfate and heating to about 40 C. The resulting latex should then bediluted to about 30-35% solids for use in tub sizing the paper.

The paper is tub sized with the cross-linked vinyl acetate polymer latexin the usual manner on the paper machine. The latex of about 30-35%solids concentration at about 90 F. is applied freely to both sides ofthe paper by passing the paper through a bath containing the latex or itcan be sprayed onto the paper. Thereafter, excess size solution can beremoved by passing the paper through press rolls and drying andcalender-ing the paper as usual. The paper can be expected to containfrom about 525% cross-linked polymer depending in part upon the solidsconcentration of the latex used, speed and temperature of applying thelatex.

The paper stock to which the vinyl acetate polymerization latex isapplied can vary widely as to fiber content but a sheet of goodformation is desirable. The weight can vary, for example, from about 4to 50 pounds per 1,000 square feet. An internal size such as rosin,aluminum stearate or a ketone dimer is useful to reduce solutionpenetration of the paper although for complete saturation by the latexthe absence of an internal size is preferable. As mentioned, theinvention is very useful with lightweight papers of about 610 pounds toavoid mottle.

The paper sized with the cross-linked vinyl acetate polymer is suitablefor sensitizing directly with photographic emulsions. However, ifdesired, the usual baryta coating may first be applied. Also, the sizedpaper can be coated on each surface with hydrophobic polymer layersbefore coating photographic emulsion layers. For this purpose,polyolefins, especially polyethylene and polypropylene, areadvantageously extruded onto the paper from a hot melt. The adhesion ofthe polymer layers applied to the sized paper at high speeds can beincreased by activating the paper surface with corona discharge asdisclosed in the Crawford et al., U.S. patent application Ser. No.630,261, filed Apr. 12, 1967. For example, sparkgap type AC corona ofabout 50,000 volts can be applied to the sized paper surface andpolyethylene extruded thereon in-line at about 200 to 1,000 f.p.m. froma melt at about 580 to 650 F. Similarly, chemical primers such aspolyethylenimine can be used to increase adhesion of the polyolefin tothe sized paper surface. Photographic emulsions, such as gelatin-silverhalide emulsions are advantageously adhered to the surface of thepolyolefin coated paper by activating the polyolefin surface with coronadischarge as described in British Pat. 971,058. Spark-gap type orcontinuous wave corona of about 50,000 volts and high frequency ispreferred and can be applied to the polyolefin surface at severalhundred feet per minute.

. The photographic emulsions which are coated upon the sized papersurface are the conventional black-and-white emulsions or a plurality ofknown differently sensitized emulsions for color photography. When colordevelopment is carried out with color development solutions containingcouplers, especially useful couplers are Couplers 1-64 listed in columns3-5 of Spath U.S. Pat. 2,956,876, issued Oct. 18, 1960 and also thecouplers as described in the same patent in column 5 as Couplers 6577 inwhich the couplers are included in the photographic silver halideemulsion layers are equally useful. Other couplers suitable for use inthe emulsions include those described in Spence and Carroll, U.S. Pat.2,640,776, issued June 2, 1953, Weissberger et a1. U.S. Pat. 2,407,210,issued Sept. 3, 1946 and Weissberger et al. U.S. Pat. 2,474,293, issuedJune 28, 1949. Other couplers which can be used in the emulsions includethe acylamino-substituted couplers, as disclosed in Salminen andWeissberger U.S. Pat. 2,423,730, issued July 8, 1947. The couplersusually produce dye images in the emulsion layers of color complementaryto the sensitivity of the respective emulsion layers. U.S. Pat.3,168,400 can be referred to for a procedure for color processing thesized papers provided with the color emulsion layers.

The accompanying drawings show in greatly enlarged cross-sectional viewthe appearance of representative photographic elements of the invention.

FIG. 1 shows a paper support sized with the crosslinked vinyl acetatepolymers and carrying a single emulsion layer 11 such as ablack-and-white gelatin-silver halide emulsion layer.

FIG. 2 shows an element wherein the sized paper 10 is provided on eachsurface with layers 12 of polyethylene, e.g. using corona discharge toadhere the polyethylene to the paper. Gelatin-silver halide emulsionlayer 11 is adhered to one of the polyethylene layers 12, e.g. by meansof corona discharge.

FIG. 3 represents a multilayer element for color photography wherein thesupport of FIG. 2 is provided with red, green and blue light-sensitiveemulsion layers which may contain the mentioned coupler compounds. Thepolyethylene surface is preferably activated with corona to effectadhesion of the emulsion layers. The vinyl acetate polymer sized papersupport of the invention is especially useful for preparing the colorproducts illustrated in FIG. 3 because the polyolefin layers 12 tend toproduce a limp paper objectionable to the customer. Adequate stiffnesscan be imparted to the product by increasing the amount of paper fiberin layer 10 by about 50% which is obviously costly. However, by use ofthe sized paper stock of the invention adequate stiffness is imparted tothe product without increase in fiber content of the paper. Thus, asshown in the examples below, a paper sheet of about pounds per 1,000square feet sized with the cross-linked polymers can be expected to havea stiffness comparable to the same type of paper of about 40 pounds per1,000 square feet not sized with the polymers.

The following examples will serve to illustrate our invention.

EXAMPLE 1 A 37-pound softwood bleached sulfite aluminum stearateinternally sized paper stock is tub sized at about 90 F. with a solidslatex of a cross-linked vinyl acetate polymer resulting from emulsionpolymerizing about 5 parts of N-methylol acrylamide and 95 parts ofvinyl acetate in the presence of catalyst and surfactant in water. Thesame paper stock is tub sized with 4% starch solution and with wateralone for comparison. The stiffness and acid penetration values of theresulting papers are shown in the following table:

Taber Valley acid Thickness stiffness penetration Size (mils) (length)(seconds) The improvement in stiffness and penetration is apparent. Thepolymer sized paper coats uniformly with gelatinsilver halidephotographic emulsion, handles well in processing and no mottle isobserved in the emulsion layer whereas the water and starch sized papersexhibit significant mottle in the emulsion layer.

EXAMPLE 2 27-pound paper not internally sized and not calendered is tubsized at about 300 f.p.m. with a 30% solids latex of the vinyl acetatepolymer of Example 1 at -90 F. and for comparison tub sized with waterand 4% starch solution. The papers have the following properties:

Taber stiffness Valley acid Thickness penetration Size L O (mils)(seconds) Water 6. 6 4. O 5. 8 91 Starch 7. 4 5. 8 197 Polymer l2. 0 6.0 5. 8 607 A paper is prepared as in Example 2 except the initial paperstock is internally sized with aluminum stearate. The stiffness of thepaper before polyethylene coating L/ C is 12.1/6.4 to l3.5/6.5 comparedto stiffness 8.0/5.0 for the same paper not polymer sized. When thispolyethylene coated paper is sensitized and processed, it shows improvedresistance to edge penetration by the processing chemicals.

This internally sized paper, tub sized with the crosslinked polymerlatex and polyethylene coated, is especially useful for coating withdifferently sensitized emulsions for color photography to produce anelement such as shown in FIG. 3. The emulsions containing color couplerscan, for example, be processed by reversal methods as shown in U.S. Pat.3,168,400 to obtain substractively colored pictures free of mottle. Theemulsions and polymer layers of the element adhere well to the sizedpaper and the paper has good feel and handling properties.

EXAMPLE 4 This example illustrates an important embodiment of theinvention wherein lightweight photographic paper stocks of about 6-10pounds are sized with the vinyl acetate polymer latex to providephotographic paper bases Unsized 3. 4 2. 1 Sized 4. 9 3. 1

The paper sensitizes uniformly with the gelatin-silver halide emulsionand handles satisfactorily in the apparatus when recording theoscillograph tracing. Mottle is not evident in the processed emulsionlayer.

In the above examples the acid penetration values are obtained by awell-known method wherein the instrument is calibrated to 40 milliampsand the test is run to a 20 milliamp end-point. The penetrating solutionis an aqueous solution of acetic acid, water and sodium chloride.

In the above examples the cross-linked vinyl acetate polymer sized papercan be coated with gelatin baryta layers prior to sensitizing withphotographic emulsions. In this case it is advantageous to include asmall amount of the vnyl acetate polymer latex into the aqueous gelatinbaryta dispersion. About 10-15% of the polymer based on the weight ofgelatin present (dry weight basis) is useful with the result thatadhesion of a gelatin-silver halide emulsion layer to the baryta coatingis improved.

The invention has been described in detail with particular reference topreferred embodiments thereof, but it will be understood that variationsand modifications can be eflected within the spirit and scope of theinvention as described hereinabove, and as defined in the appendedclaims.

We claim:

1. A light-sensitive photographic paper comprising a paper support tubsized with an emulsion polymerized mixture of from about 90 to 99.5% byweight of vinyl acetate and about 10 to 0.5% by weight of aethylenically N-methylol acrylamide or N-methylol methacrylamide or amixture thereof.

4. The paper of claim 1 wherein an extruded polyolefin layer separatesone surface of the sized paper support from the emulsion layer and theother surface of the sized paper carries an extruded polyolefin layer.

5. The paper of claim 4 wherein the polyoleln is polyethylene orpolypropylene.

I 6. The paper of claim 2 wherein the paper support before tub sizinghas a weight of about 5 to pounds per 1,000 square feet.

7. The-"paper of claim 2 wherein the paper support before tub sizing hasa weight of about 6 to 10 pounds per 1,000 square feet.

8. The paper of claim 2 wherein a baryta coating separates one surfaceof the sized paper from the emulsion layer.

9. The paper of claim 5 wherein one surface of the polyoleln coatedpaper carries differently sensitized superposed silver halide emulsionlayers useful for color photography.

I References Cited UNITED STATES PATENTS 2,748,029 5/1956 Spear et al.968S 2,721,801 10/1955 Clark et a1 96--85 3,062,679 11/ 1962 Heardle etal 9685 3,161,519 12/1964 Alsup 96-85 2,928,736 3/ 1960 Laakso et a1.96-85 3,369,901 2/1968 Fogge et a1 96-85 NORMAN G. TORCHIN, PrimaryExaminer E. C. KIMLIN, Assistant Examiner U.S. Cl. X.R. 96--87; 162-168

